Ballast device



Feb. 6, 1934. c. P. BROCKWAY BALLAST DEVICE Filed Sept. '7, 1928 INVENTOR 0m E/PUCKW/IV BY Mai, 4 a it",

ATTORNEY Patented Feb. 6, 1934 BALLAST DEVICE Carl P. Brockway, Ridgewood, N. J., asslgnor to World Bestos Corporation, Paterson, N. 1., a corporation of Delaware Application September 7, 1928. Serial No. 304,397

Claims.

This invention relates to ballast devices adapted to be used in compensating for variations of voltage in electric circuits, and particularly in filament circuits forvacuum tubes used in radio 6 apparatus.

In radio receiving apparatus designed to use current supplied by the ordinary electric lighting power circuits, some difficulty has been experienced in providing tubes that would operate efilciently on this power supply, owing to the fact that the voltage of an ordinary electric lighting circuit generally varies in the neighborhood of twenty or thirty volts. Variation of the voltage of the circuit causes the tube to use more or less current, with the result that the temperature of the filament, and therefore the operation of the tube, is caused to vary. In some tubes where a filament having a positive temperature coefiicient is used, there is considerable danger to the life of the tube in this voltage variation of the line. Such a filament having a spot of increased resistance therein will deteriorate at that spot, owing to the large current which will flow through it when the resistance is decreased due to a cooling down of the filament. In fact, by actual test, it has been found that the lives of such tubes are considerably shortened for this very reason.

It is therefore one of the principal objects of this invention to provide a simple device which, when used in connection with vacuum tubes, will have a compensating action for variations in line voltage, with the result that the current flowing through the filament of the vacuum tube is substantially constant.

Another object of the invention is to provide a ballast device which will draw a minimum amount of energy from the line while producing a maximum ballasting efiect on the filament of a vacuum tube with which it is used.

Another object of the invention is to provide a ballast device which will have a relatively long life.

A still further object of the invention is to provide a ballast device which is compact and attractive in appearance and adapted to be easily associated with a standard radio set.

Other objects will be apparent as the description of the invention proceeds.

The invention has been illustrated in the accompanying drawing, in which Fig. 1 is a sectional side elevation of a ballast device embodying the invention;

Fig. 2 is a sectional side elevation of a modification of the ballast device shown in Fig. 1; and

Fig. 3 is an enlarged sectional view through the ballast wire.

Referring now more specifically to the drawing, the invention comprises a glass envelope 10 mounted on a standard four terminal radio tube 60 base 11. A re-entrant press 12 has a pair of conductors 13 sealed therein which are connected to the ballast wire 14 mounted inside of the envelope. The ballast wire 14 is a resistance wire having a relatively large resistance variation in 66 response to temperature changes in the neighborhood of the operating temperature of the device and is preferably made of iron and plated with chromium and is looped back and forth over wire supports 15 and 16 which are in turn welded 7c in the glass beads 17 and 18, respectively, mounted on a glass rod 19 which is supported in the press 12. The method of mounting the wire is similar to the method of mounting the lighting filament in a standard electric light bulb. The envelope 10 is filled with an inert gas, nitrogen having been found excellent for this purpose, although other gases, such as argon, helium, and neon may be used to good advantage.

The inner surface of the envelope 10 for a portion of the distance up from the base 11 is covered with a silvered coating 20 which may be put on, if desired, by flashing magnesium after the tube has been exhausted, as is the standard practice with ratio vacuum tubes.

The conductors 13 are brought through the stem and connected to any two terminals on the base, the drawing showing such connection being made to what would ordinarily be the grid terminal 21 and its diagonal filament terminal 22.

A series of radio tubes 23 are shown in Fig. l with their filaments connected in parallel. and in series with the ballast tube and with the secondary of a transformer 24, the primary of which may be connected to a source, 25 of alternating current.

In the modification shown in Fig. 2, the iron wire is first coiled and then mounted in a double helix around a glass stem 26 which is provided with supports 2'7 sealed therein and maintaining the coiled helix in position inside of the envelope.

The advantage of chromium plating iron wire to be used for ballast purposes is that the chromium plating forms a hard shell which mechanically protects the wire from the evolution of gases and oxidation. Iron wire has been used for ballast before, but when such iron wire is used in the atmosphere, the temperature must be raised to a high degree in order to give the desired ballasting effect, as the resistance of the wire in- 110 creases more at higher temperatures with variations of current. The life of a ballast wire, therefore, in the open air is relatively short, inasmuch as in the high temperatures oxidation takes place, with the result that the wire is gradually burned up. Chromium plating the wire overcomes, to a large extent, this oxidation and burning up of the wire, but it is still necessary to maintain the wire at a high temperature to get the desired ballasting effect. I have found, however, that if the ordinary atmosphere is removed from the wire, not only is oxidation prevented, but the desired ballasting effect may be had at relatively low temperatures. If oxygen and other atmospheric gases are removed from the vicinity of the wire, there must still be some means of dissipating the heat energy therein. or the temperature of the wire will build up, and hence I have found that an inert gas, such as nitrogen, gives good results in carrying the heat from the wire to the glass envelope, where it is dissipated into the atmosphere.

Where exposed iron wire is contained in a vacuum or in an inert gas constant heating of the wire under excess voltages and under normal voltages causes vaporization of the metal at the surface. Under continued use the wire is therefore decreased in diameter at its weakest point until such time as the wire parts. A coating of chromium on the wire, it has been found, serves to retain these particles in position and prevent vaporization.

Due to the convection currents of this gas, the upper part of the tube, when the tube is used in a vertical position, naturally becomes hotter than the lower part, with the result that the lower loops of the iron wire are considerably cooler than the upper loops. This tends to heat the wire unevenly and cause the upper loops of the wire to deteriorate at a quicker rate than the lower loops. In order to make a more even heating of the ballast wire, I have provided the magnesium surface on the lower inner surface of the envelope. This surface reflects heat from the wire back on to the wire again and maintains the lower loops of the wire, therefore, at a higher temperature than they would be if clear glass alone were used in the envelope.

While the invention has been described and illustrated in connection with a radio circuit, it is to be understood that the ballast tube may be used wherever a ballasting effect is desired, and I do not, therefore, desire to limit the invention to the specific construction shown, except as defined in the appended claims.

What I claim is:

1. In a compensating device for voltage variations, an envelope, a relatively long iron wire within said envelope, said wire being encased in a shield of chromium an inert gas surrounding said wire, and a reflecting surface on the euvelope whereby heat from the wire is reflected back into the envelope.

2. In a compensating device for voltage variations, an envelope, a resistance wire within said envelope having a relatively large variation of resistance for changes in temperature, said wire being encased in a shield of chromium, an inert gas within said envelope and surrounding said wire, and a reflecting surface on the envelope at one end thereof whereby heat from the wire is reflected into the envelope.

3. In a compensating device for voltage variations a substantially sealed envelope, a wire within said envelope having a relatively large resistance variation for changes in temperature. said resistance wire being formed of iron, a coating of chromium covering said wire, an inert gas fllling said envelope and surrounding said wire, and a magnesium coating on the inner surface of the envelope adjacent the bottom thereof whereby heat generated from said wire at the lower portion thereof will be reflected back to said wire.

4. In a resistance device an elongated envelope adapted for positioning normally in a vertical position, a resistance element mounted within and along the axis of said envelope, said element being adapted for heating by the passage of an electric current therethrough, an inert gas within said envelope, and a reflecting surface on the lower portion of said envelope for reflecting heat radiated from the filament into said envelope and upon the adjacent portion of said element.

5. In a resistance device an elongated envelope adapted for placement in a vertical position, a reflecting surface on said envelope adjacent one end of and within the envelope, a resistance element within said envelope and extending in the direction of elongation thereof, and an inert gaseous substance within said envelope, said reflecting surface being adapted to reflect heat derived from said element into the envelope.

CARL P. BROCKWAY.

III

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